The SU25 cannon sound has changed since the 1.05 patch. It sounds now like a buzzing noise which doesnt sound very lethal at all and takes away the immersion when you hear a friendly Su25 flying over buzzing away as it gun runs some targets. I dont know if this change was intentional, but since it is also a 30mm cannon like that of the A10, without it being a rotary one admittedly, one would think that it would have a similar sound when fired.